This invention relates to a method and apparatus for hydraulically controlling a fan associated with a fluid cooling system for a heat exchanger, high performance hydraulic working system, or the like.
In the past, various hydraulic systems have been known which are operable to drive a cooling fan for a heat exchanger. In one previously known system, a fixed delivery hydraulic pump is used to drive a hydraulic motor and cooling fan for an internal combustion engine. A relief valve is interposed in the hydraulic circuitry between the pump and motor and is operably connected to a temperature sensor which monitors the engine cooling system temperature. If the cooling system temperature is within a prescribed temperature range, hydraulic fluid from the pump is permitted to bypass the fan motor. In the event, however, the temperature of the cooled fluid exceeds a prescribed value, the relief value is actuated increasing pressure and thereby increasing the amount of working fluid delivered to the fan motor.
Although such a control system has at least a degree of theoretical appeal, a general disadvantage is that the input power to the pump comprises that utilized by the fan as well as that wasted in the fluid bypassing the relief valve, and that the energy of the wasted fluid is converted into heat within the hydraulic circuit.
Other previously known systems tend to provide for on-off control or control at various levels depending upon the cooling system temperature conditions. Although these systems have a place in the industry, variable control is highly desirable in many circumstances.
The difficulties suggested in the preceding are not intended to be exhaustive, but rather are among many which may tend to reduce the effectiveness of prior methods and apparatus for hydraulically controlling a cooling fan. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that hydraulic control systems appearing in the past will admit to worthwhile improvement.
In the above connection, it would be highly desirable to provide a method and apparatus for driving and controlling a cooling fan which absorbs a minimum amount of power from the hydraulic drive, hence creating a minimum amount of power loss and heat generation. It will also be desirable to provide a control system wherein the hydraulic line from the pump to the motor is direct and does not require the insertion of devices to measure flow from the pump.